Narrowband heterodyne reception using unstabilized sources

Source power for laboratory-type experiments is often limited at millimeter and submillimeter wavelengths. This requires the use of sensitive receiving equipment. Cooled square-law detectors and narrowband heterodyne detectors are examples. We have developed a coherent mechanical frequency shifter, which makes possible narrowband heterodyne detection without the need for highly frequency stable sources. Identical frequency and phase fluctuations of the transmit and local oscillator signals derived from one source are eliminated at the intermediate frequency. The widely tunable frequency shifter, designed for a 637GHz scale-model radar, was tested in a 140GHz non-radar configuration. We investigated the receiver's minimum coherently resolvable bandwidth and its sensitivity. Several types of sources were compared for the effect of local oscillator amplitude noise on receiver sensitivity at low intermediate frequency.     

A coherent mechanical submillimeter frequency shifter

Highly correlated transmit and local oscillator signals for use in a narrowband heterodyne system are derived from a single submillimeter source. One component is Doppler shifted in frequency by a mechanically rotating device before transmission. The frequency translation does not lead to significant spectral deterioration. Under the condition of only a small differential delay between transmit and local oscillator paths, most phase and frequency instabilities of the submillimeter source are eliminated at the intermediate frequency. The paper describes the frequency shifter's mode of operation and a practical 637GHz design. Based on this design we simulate the effect of various imperfections in the frequency translation process on the output spectrum. Preliminary measurements at 140GHz are included.     

High frequency GaAs nano-optomechanical disk resonator

Optomechanical coupling between a mechanical oscillator and light trapped in a cavity increases when the coupling takes place in a reduced volume. Here we demonstrate a GaAs semiconductor optomechanical disk system where both optical and mechanical energy can be confined in a subwavelength scale interaction volume. We observe a giant optomechanical coupling rate up to 100 GHz/nm involving picogram mass mechanical modes with a frequency between 100 MHz and 1 GHz. The mechanical modes are singled-out measuring their dispersion as a function of disk geometry. Their Brownian motion is optically resolved with a sensitivity of 10(-17) m/√Hz] at room temperature and pressure, approaching the quantum limit imprecision.     

A two-stage optical frequency comb generator based on Mach-Zehnder modulator and Re-circulating frequency shifter

We propose a novel scheme to generate optical frequency comb by using a two-stage generator based on Mach-Zehnder modulator and re-circulating frequency shifter. Based on the Mach-Zehnder modulator a light source including 2 flat and stable frequency spectrum lines is generated at the first stage, and the light source is then used as the seed light in the re-circulating frequency shifter loop at the second stage. The scheme can greatly reduce the accumulated noise of the system. Through theoretical analysis and simulation it is shown that the proposed theoretical model of the two-stage system is proved in good agreement with simulation results.     

SEMICONDUCTOR-SUPERLATTICE FREQUENCY MIXER FOR DETECTION OF SUBMILLIMETER WAVES

We report on a GaAs/AlAs superlattice frequency mixer for detection of submillimeter waves. The mixer is based on the nonlinear miniband transport giving rise to domains excited under the action of a microwave field. We designed the mixer for broadband operation (300–600 GHz). For studying basic properties, we investigated the mixer as a harmonic mixer in 15^th order to detect radiation at a radio frequency (RF) near 300 GHz using local oscillator (LO) radiation of a frequency near 20 GHz. We reached a noise equivalent power (NEP) of about 10 fW/Hz. We also show that the use of the superlattice mixer together with a superlattice frequency multiplier allows to realize a superlattice-based free-space transmission line for submillimeter waves.     

Demonstration of microwave frequency shifting by use of a highly chirped mode-locked fiber laser

We report an experimental demonstration of a photonic microwave shifter using a highly chirped mode-locked fiber laser. The system is based on dispersive compression or expansion of highly chirped optical pulses that are amplitude modulated by the microwave signal. Using this technique, we demonstrated frequency shifting of a microwave signal from 10 GHz down to 5 GHz and up to 25 GHz.     

Frequency synthesizers up to 370 GHz

A new generation of frequency synthesizers up to 370 GHz is described. The main parts of them are microwave frequency synthesizer covering 11–15 GHz band, effective frequency multipliers-mixers using an opposite pair of planar Shottky diodes and a lock-in loop of a backward-wave oscillator tube covering millimeter and longer part of submillimeter wave bands with tens of milliwatts of output power. The ways of further increase in the operating frequency of such synthesizers are discussed.     

Frequency pulling in an optically pumped submillimeter laser by Doppler induced dispersion

The dependence of the frequency of a CW optically pumped submillimeter laser on the frequency of its pump laser has been directly measured and shown to result largely from the dispersion produced by the two peaked gain spectrum resulting from pumping in the wings of a Doppler broadened absorption line.     

同轴插板式相移器数值模拟与实验研究

 根据同轴插板式相移器的基本工作原理,对该相移器进行了数值模拟与优化设计,并重点研究了其结构工艺和相移控制方式。在此基础上研制了一个中心频率为4.1 GHz的相移器模型,并通过矢量网络分析仪进行了实验测量。测量结果表明：在4.0～4.2 GHz的频带范围内,该相移器可实现90°的相移量,相移量化精度为1°,相移精度为±１０°,相移器插损1.5 dB。     

A GaAs planar Schottky varactor diode for left-handed nonlinear transmission line applications

The left-handed nonlinear transmission line(LH-NLTL) based on monolithic microwave integrated circuit(MMIC) technology possesses significant advantages such as wide frequency band,high operating frequency,high conversion efficiency,and applications in millimeter and submillimeter wave frequency multiplier.The planar Schottky varactor diode(PSVD) is a major limitation to the performance of the LH-NLTL frequency multiplier as a nonlinear component.The design and the fabrication of the diode for such an application are presented.An accurate large-signal model of the diode is proposed.A 16 GHz-39.6 GHz LH-NLTL frequency doubler using our large-signal model is reported for the first time.The measured maximum output powers of the 2nd harmonic are up to 8 dBm at 26.4 GHz,and above 0 dBm from 16 GHz to 39.6 GHz when the input power is 20 dBm.The application of the LH-NLTL frequency doubler furthermore validates the accuracy of the large-signal model of the PSVD.     

全光纤激光多普勒测速技术的研究

介绍一种全部采用普通单模光导纤维作为光路的激光多普勒测速系统.在该系统中采用普通单模光纤声光频率偏移装置实现被测流场速度方向的判别;以单模光纤偏振控制器控制光纤中激光偏振态,与常规激光多普勒测速系统相比,该系统结构简单,体积小、调整方便,而且测速探头具有极好的移动灵活性.     

Observation of Frequency Down-Shift in a Submillimeter Wave Gyrotron

Frequency down-shift in the initial stage of CW or long pulse operation of a submillimeter wave gyrotron, Gyrotron FU IV, is observed. The shift occurs in a few minutes after turning on the operation and the amount of the shift attains even 0.1 GHz. The observation results are analyzed on the basis of a simple model for heat conduction in the region of a resonant cavity. The frequency shift is explained consistently by expansion of the cavity.     

Scaled model measurements of the sandwiched V-antenna

At frequencies above a few hundred GHz, waveguide mixer blocks become extremely difficult to build, so open structure feeds may be more appropriate. One promising planar antenna structure, which can easily be integrated with SIS junctions, is the sandwiched V-antenna. The antenna is completely enclosed in dielectric by placing it between substrate and superstrate blocks. Using a model scaled to a center frequency of 10 GHz, we investigated the beam pattern as a function of frequency, and measured its dependence on gaps between the super-and substrates. We plan to test the structure at a frequency of 345 GHz and to compare it with waveguide horn antennas for possible use in submillimeter astronomical receivers. The antenna patterns and analysis in this work are substantially more extensive than earlier published results.     

Fast quasi-optical phase shifter based on the effect of induced photo conductivity in silicon

We study, both numerically and experimentally, a microwave commutator (phase shifter), whose active element comprises a metal plane mirror with a semiconductor plate on it. Phase shifting of the reflected microwave beam is attained by creating a conducting layer in the semiconductor by a laser with quantum energy approximately equal to the forbidden band width. Using a disk of high-purity silicon and a titatnium-sapphire pulsed laser, we study experimentally a 180° phase shifter operated with a Gaussian wave beam at a frequency of 30 GHz. Efficient phase shifting of the wave beam over a time of several nanoseconds is shown at a low power level.     

Metal mesh couplers using evanescent waves at millimeter and submillimeter wavelengths

In this paper we introduce a metal mesh evanescent wave coupler that makes use of evanescent wave coupling between a metal mesh and a dielectric plate, as a quasi-optical component for millimeter and submillimeter wavelengths. The transmission properties of this type of couplers have been investigated experimentally and theoretically for both capacitive and inductive metal meshes in the frequency range from 40 GHz to 60 GHz. The transmittance of a capacitive metal mesh evanescent wave coupler can be adjusted more than 70% by changing the spacing between the capacitive mesh and the silicon plate less than 0.15 mm at around 57 GHz.     

轴向加速管的数值模拟

 用二维全电磁数值模拟方法研究了轴向加速管，虽然没有实现理想群聚，但通过加一个中间腔, 大大提高了前两阶谐波电流分量，其中一阶谐波电流调制系数达到了140%，二阶谐波电流调制系数达到了68%。通过对提取腔的设计，可以选择地输出不同的频率，其中一次谐波频率为2.2GHz,输出功率1.25GW，效率9.33%；二次谐波频率为4.4GHz，输出功率0.48GW,效率3.6%。     

Production of an Intense, Well-Collimated Submillimeter Wave Beam and Its Application to Plasma Scattering Measurements

Intense submillimeter wavelength radiation (f=354 GHz, P=110 W) from Gyrotron FU II is converted into a well-collimated, linearly-polarized beam by a quasi-optical transmission line consisting of a quasi-optical antenna and several mirrors. The observed focusing of the beam agrees with calculations based on the Huygens equation. We have used this intense beam to study low frequency density fluctuations by plasma scattering in Compact Helical System (CHS) plasmas at the National Institute for Fusion Science.     

Weibull Raindrop-Size Distribution and its Application to Rain Attenuation from 30 GHz to 1000 GHz

A weibull raindrop-size distribution is fitted to the measurements of rainfall observed using a distrometer in Tokyo. A propagation experiment at 103 GHz is also introduced. The rain attenuation is calculated by considering the Mie scattering for the Marshall-Palmer, Best, Joss-Thomas-Waldvogel, Gamma and Weibull raindrop-size distributions. The results of frequency characteristics from the Weibull raindrop-size distribution agrees well with some experimental data for the millimeter and submillimeter waves above 30 GHz. The quick read table is calculated for the rain attenuation from 30 GHz to 1000 GHz.     

Spurious Signal Response of Broadband Solid–State Frequency Multipliers at Millimeter and Submillimeter Wavelengths

Heterodyne instruments at millimeter and submillimeter wavelengths often use wideband fixed-tuned frequency multipliers, in conjunction with broadband power amplifiers driven by frequency synthesizers, as the local oscillator (LO) source. At these frequencies the multipliers use Gallium Arsenide (GaAs) based Schottky varactor diodes as the nonlinear element, and like most other harmonic generators are susceptible to spurious signal interference. The state-of-the-art LO sources at these wavelengths use high power MMIC amplifiers at the initial stages, and are used to drive the subsequent multiplier stages to have enough LO power to pump the mixers. Because of the high input power environment and the presence of noise in the system, the multipliers become vulnerable to spurious signal interference. As the spurious signals propagate through the receiver system, they generate inter-modulation products which might fall in the passband of the heterodyne instrument and seriously degrade its performance. In this paper spurious signal response of solid-state frequency multipliers at millimeter and submillimeter wavelengths is investigated. Results of numerical harmonic balance simulations and laboratory experiments, which were found to show good agreement, are presented here.